Method of assembling a control having a body member and a cover member with an access aperture therein

ABSTRACT

A control assembly for hydrostatic transmission having a valve controlling the flow of fluid to the pump includes a pump body member having a cavity with a moveable valve element mounted in the body and connected to a fluid pressure source, and having a neutral position. Linkage including an upstanding pin interconnects the pump to the valve element. A cover extends over the body and is secured thereto. A control shaft extends through the cover having an exterior end with a manual control lever mounted thereon, and an interior end to which a cam plate having an elongated cam slot therein is secured. A detent portion in the cam slot opposite to the upstanding pin defines a neutral position for the pin. A screw adjusts the valve element into a neutral position. A torsional spring in the cover yieldingly holds the control shaft, the control lever, the cam plate, the valve element, and the remainder of the linkage in a neutral position. The method of assembling the control assembly involves placing an elongated alignment tool on the upstanding pin and moving the tool into a prepositioned cam slot detent, placing the cover on said body and extending said tool through an aperture in the cover; securing the cover to the body, and removing the tool.

This is a divisional of U.S. application Ser. No. 08/049,988 filed Apr.16, 1993 now U.S. Pat. No. 5,378,127.

BACKGROUND OF THE INVENTION

Dual path vehicles require two hydrostatic transmissions per vehicle.One transmission drives the left propel wheels or track, and the othertransmission drives the right propel wheels or track. Each transmissionhas a separate control lever to stroke the transmission for the operatorcommand station. Thus, if the operator pushes both control leversforward an equal amount, the operator expects both transmissions toprovide the same output so the vehicle will go straight ahead. If onetransmission provides a greater output than the other, the vehicle willbegan to steer to one side or the other. The symmetry from the left tothe right transmission is the most important when the operator isleaving neutral and when the operator reaches full stroke. Near neutralis important because if the operator is trying to inch forward veryprecisely, both transmissions should (left propel and right propel)start moving at the same time. If they do not move at the same time thevehicle will index to one side making it very difficult to do preciseinching. Likewise with the handle at maximum angle, both transmissionsneed to have the same output or the vehicle will not go straight, buttend to steer opposite to the transmission with the greatest output.

Symmetry is also important on single mode transmissions to a lesserdegree. The user expects equal output from the transmission regardlessof whether the handle is moved in the forward or reverse direction.

To meet desired requirements of a larger neutral dead band and smoothcontrol near the neutral position, it is desirable to incorporate a camto tailor the movement of the valve spool relative to input handle. Thistailored movement will optimize the vehicle controllability. It is alsodesirable to spring center the input handle to isolate any clearance orbacklash in the vehicle control linkage from affecting the performanceof the transmission.

However, spring centering the handle can create a problem with symmetryfrom forward to reverse. If the transmission control linkage orhydraulic valve spool are adjusted to ensure that the spool is centeredin the neutral porting position, it does not assure that the handle iscentered in the cam dead band. Likewise, if the handle is centered, thisdoes not assure that the spool is centered.

When such vehicles are going downhill, the hydraulic motor in thetransmission starts pumping oil to the pump. This backlash action causesthe motor to override the pump and the vehicle speeds up. This can becounteracted by the valve spool in the hydraulic control, but the spoolis slow to react because of accumulated tolerances in the controllinkages and in the linkage on the equipment.

It is therefore a principal object of this invention to symmetricallycenter the control handle of the hydrostatic transmission control, andto eliminate all accumulated tolerances in the linkage system.

A further object of this invention is to provide a method of assembly ofthe hydraulic transmission controls which will precisely center thecontrol lever in the center of the dead band.

These and other objects will be apparent to those skilled in the art.

SUMMARY OF THE INVENTION

The control assembly for hydrostatic transmissions of this inventionincludes a pump and a valve element to control flow of hydraulic fluidto the pump. The control assembly includes a body member having a cavitywith a moveable valve element mounted in the body and connected to asource of hydraulic fluid under pressure, and, having a neutralposition. Linkage means including an upstanding pin interconnects thepump to the valve element. A cover member extends over the body memberand is secured thereto. A control shaft extends through the cover memberand has interior and exterior ends. A manual control lever is mounted onthe exterior end of the control shaft, and a cam plate is secured to theinterior end of the control shaft. The cam plate has an elongated camslot therein. A detent portion is located in the cam slot and receives aguide sleeve to define a neutral position whereby the upstanding pinwill also be in a neutral position.

A resilient torque spring in the cover yieldingly holds the controlshaft, the control lever, the cam plate, and the remainder of thelinkage means in a neutral position. The neutral position of the valveelement is determined by an adjustment screw.

The method of assembly of the control assembly involves placing anelongated alignment tool on the upstanding pin, moving the alignmenttool into the detent of the cam to orient the upstanding pin in aneutral position, placing the cover member on said body member andextending said tool through an access aperture in the cover member;securing the cover member to the body member, and removing the alignmenttool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a skid loader which is a typical vehicleupon which this invention is used;

FIG. 2 is a plan view of the control assembly;

FIG. 3 is a partial perspective view of the hydraulic valve spool andrelated control linkage elements;

FIG. 4 is an elongated sectional view taken through the central assemblycover during assembly, as taken on line 4--4 of FIG. 2;

FIG. 5 is a sectional view similar to that of FIG. 4 after assembly iscompleted;

FIG. 6 is a plan view similar to that of FIG. 2 but with the controlassembly cover removed;

FIG. 7 is a sectional view taken on line 7--7 of FIG. 2;

FIG. 8 is a partial sectional view taken on line 8--8 of FIG. 7;

FIG. 9 is an enlarged scale partial plan view of a portion of FIG. 6when the guide sleeve is inserted; and

FIG. 9A is a plan view similar to FIG. 9 with the guide sleeve removed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The numeral 10 designates a conventional skid loader which typicallywould employ this invention. The skid loader 10 has a frame 12 with twowheels 14 on each side, a cab for the operator, and a typical front endloader 18 comprised of a bucket 20 and hydraulic cylinders 22. Skidloader 10 normally will have the wheels 14 on opposite sides thereofdriven by separate hydrostatic transmissions. The manual displacementcontrol for hydrostatic transmissions of this invention will beapplicable to such a vehicle.

Manual displacement control assembly 24 includes a control assemblycover 26 (FIGS. 2, 4, 5 and 6) and a pump body 28 (FIGS. 7 and 8). Aconventional valve spool 30 is slideably mounted in a suitable bore 31(FIG. 8) in body 28 (FIG. 7) and should have spring 32 (FIG. 3) mountedon one end thereof so that the spring can remove the backlash from thelinkage. As discussed hereafter, spring 32 will serve to take the slackout of the linkage system whereby the hydrostatic transmission iscontrolled.

A cavity 34 (FIG. 7) appears in body 28 and contains a horizontal arm 36(FIGS. 3 and 7) which is pivotally connected at 38 to body assembly 40.End 42 of arm 36 (FIGS. 3 and 7) is connected to a conventionalswashplate 43 of transmission pump 43A. The numeral 43B designates theservo piston of the pump, and the numeral 43C designates a bearing forswashplate 43. End 44 of arm 36 has a first upstanding pin 46 which ispivotally mounted in bearing 48 of horizontal arm 50 (FIG. 7). Ahorizontal U-shaped connector 52 engages planar sides 54 (FIG. 3) ofvalve spool 30 so as to conventionally move spool 30 in a longitudinaldirection to effect and control the flow of hydraulic fluid in themechanism.

A second upstanding pin 56 extends from arm 50 and extends through anelongated cam slot 58 in cam plate 60 (FIGS. 3 and 6). Cam slot 58 hasends 62 and 64 with a centrally located arcuate detent 68 on one sidethereof as best shown in FIGS. 3 and 6. The adjustment screw 40A isthreaded into the body 28 by threads 41. Rotation of the adjustmentscrew will pivot assembly 40 (FIG. 7) around screw 40B (FIG. 7). Asassembly 40 pivots around screw 40B, pin 38 (FIG. 7) moves back andforth and via arm 36 and arm 50, the spool (30) is centered in theneutral porting position.

With reference to FIGS. 4, 5 and 7, a vertical disposed control levershaft 70 extends downwardly through a sealable aperture in cover 26.Shaft 70 has an upper end 72 which protrudes from the cover 26 and hassuitable serrations therein. Shaft 70 extends downwardly through anannular boss 74 in cover 26 and is rotatable within the boss. The lowerend of shaft 70 is rigidly secured at 76 to cam plate 60. A suitablehandle control 78 is mounted on the upper end 72 of shaft 70.

With reference to FIGS. 2, 4 and 5, a threaded aperture 80 appears incover 26 and is adapted normally to be closed by screw plug 82 as shownin FIG. 5. A plurality of retention bolts 84 (see FIG. 7) are adapted tosecure cover 26 to body 28.

An elongated guide sleeve 86 has an aperture 88 in the lower end thereofwhich can be inserted over pin 56. As described hereafter, when plug 82is removed from threaded aperture 80, guide sleeve 86 can be extendthrough aperture 80 as shown in FIG. 4 when the cover 26 is mounted onbody 28.

With reference to FIG. 7, a pin 90 extends downwardly into the cavity 91which surrounds boss 74. A torsion spring 92 is mounted on boss 74 andhas opposite ends 94 and 96 which are bent slightly towards each otherbut which are laterally spaced apart from each other. As seen in FIG. 6,ends 94 and 96 extend outwardly from the body 97 of spring 92 in aparallel direction. Ends 94 and 96 embrace the sides of downwardlyextending pin 90 as well as the upwardly extending tang 61 which is apart of cam plate 60. This arrangement of structure fixes the cam plate60 in a neutral position. Also, torsion spring 92 returns the spool 30to neutral porting position.

The detent 68 is so positioned in cam slot 58 that it will maintain thepin 56 in the neutral position of the cam plate 60 when the guide sleeve86 is nestled in detent 68.

With reference to FIG. 2, the control handle 78 is normally moved fromthe position shown in FIG. 2 in a clockwise direction approximately 33degrees to effect movement of the vehicle in a first direction, and ismoved in a counter-clockwise direction from the position in FIG. 2 toeffect movement of the vehicle in an opposite direction. A dead bandzone of handle 78 is defined as an arc of approximately one half to oneand one half degrees in either direction from the neutral position shownin FIG. 2 wherein no movement of the vehicle will take place in eitherdirection.

Before the cover 26 is placed on body 28, guide sleeve 86 is mounted onthe upper end of pin 56 as shown in FIG. 4. Thus, if pin 56 ismisaligned as shown by the dotted lines in FIG. 9, guide sleeve 86 willdraw pin 56 to the neutral position seen in FIG. 9A opposite detent 68.Spring 32 acting through spool 30, connector 52 and arm 50 holds pin 56against the inner edge of cam slot 58. The guide sleeve 86 is used toalign the cam 60 during installation to the center of the dead band zoneas described above and as depicted by the position of handle 78 in FIG.2. The guide sleeve 86 snugly embraces the detent 68 in cam slot 58 tohold pin 56 in neutral alignment with detent 68. This maintains pin 56in the neutral position within cam slot 58. The cover 26 is theninserted on body 28 as shown in FIG. 4 with the guide sleeve 86protruding through aperture 80. The bolts 84 (see FIG. 7) are thentightened to lock the control cover in place. The guide sleeve 86 isthen vertically removed and the plug 82 is used to close the aperture80. The control handle 78 can then be used to stroke the linkage.

It should be noted that the spool 30 is moved to a neutral portingposition after the guide sleeve 86 is used to align the cover 26. Asdescribed above, the guide sleeve 86 is used to align the pin 56 withdetent 68 in the center of the cam deadband before the spool 30 isadjusted to neutral. After the guide 86 is removed, and the cover 26 issecured to the housing, then the adjustment screw 40A is used to movethe spool via the linkage to a neutral porting position.

The spring 32 acts in conjunction with spool 30 to serve as a backlashspring that takes out the tolerance in all the linkage joints betweenthe spool 30 and the cam 60. This loads the pin 56 to one side of thecam slot 58 so that the pin will not hang up in the detent 68 when thehandle 78 is operated during the normal operation of the vehicle. Again,the guide sleeve 86 ensures that all of the linkage between the spool 30and the cam 60 are in a neutral position when the cover 26 is mounted onthe body 28.

It is therefore seen that the device of this invention will achieve atleast its stated objectives.

I claim:
 1. A method of assembling a control assembly having a bodymember with a cover member securable to said body member, said covermember having an access aperture therein, said access aperture being insubstantial alignment with a second upstanding pin on linkage meansdisposed within said body member the method comprising:placing anelongated alignment tool on said second upstanding pin; placing saidcover member on said body member and extending said tool through saidaccess aperture; securing said cover member to said body member; andremoving said alignment tool.